Define "windows". There are port shades that attach above hull portholes that prevent almost all rain from entering. Overhead hatches are more difficult, but search the web for some complicated cloth dorade-type things that allow this.

If the windows in question are hatches, we made a dorade concepthatchdodger for our forehatch. It can be left open in up to 15 k. without rain coming in, or lowering the hatch. (Our reefed position for this hatch is one long champagne cork.) If we need to totally close it, it will be very windy, and cold.

Ann

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Ann, with Jim, aboard US s/v Insatiable II, in Oz, very long term cruisers

This was ages ago, & I'm going from memory, but... I've seen some, which were most likely DIY affairs. They were akin to clam shell vent covers. But were made out of canvas, with short sections of tent poles sleeved into thier lower ends to keep them propped open. And the poles ends were fitted into small "socket" pieces on the cabin house side. On either side of each port, I mean. And it was the tension on/from the poles, which kept the port covers open.
Ah, their upper sides were simply slotted into boltrope tracks, above the ports.

I'd imagine that one could run bolt rope track with which to attach the canvas to, almost 180 degrees around the port if you liked. And how long of a pole which you use would be the governing factor in terms of how far out from the cabin side they protruded.
The tricky part would be getting the cut of the cloth correct, so that they stick out far enough, & yet still have clean shapes to them. Which would likely involve a bit of trial & error.

__________________The Uncommon Thing, The Hard Thing, The Important Thing (in Life): Making Promises to Yourself, And Keeping Them.

One caveat, check carefully before final stick down! I dumbly neglected to notice that the hinged opening lid of our aft side deck lazarette lockers would not completely clear the installed 'eyebrows'. After discussion with Seaworthy, who are truly helpful people, I was able to use a cordless Dremel on the installed eyebrows ( ONE each side of the after cabin of our centre cockpit boat)Dremel tool fitted with a side cutting bit, like a drill bit, but used for cutting tiles perhaps, and nibbled just enough from the corner to allow the locker lid to pass yet not remove the moulded in drip edge of the eyebrow. The variable speed Dremel was set to run at half speed so as not to melt the Lexan.

Our opening ports were made by Lewmar and had an inherent design defect that allowed water to enter the outer (hollow) frame via a horizontal join in the extrusion then run inside to exit at an unused screwhole into the interior, by wayof thelocking lever. This design error ran for nearly 18 years but was removed on the later designs. We had tried to remedy the leak by the Lewmar recommended solution of removing the existing frame joint sealant with a 'pick' and replacing it with fresh goo but that was only 90% successful as in tropical downpours some stlll got through. however since fitting the Seaworthy Eyebrows the problem is completely resolved, plus we can open the ports for ventilation in rain ( their true purpose) as a bonus.

Your advice is very good:
"One caveat, check carefully before final stick down!"

On our blog post we show how we taped into final position to test everything. Once confirmed, we just lifted the covers using the tape hinges, removed the backing tape, and lowered them into final, glued position.

If you have round port holes, there is a cheep fix. Plastic waste paper bins are usually tapered. Find one that can be pushed into the port, but gets snug before it goes all the way through. Once you have the right size, take it back and cut a square out of the side of the bin. Now shove it back into the port with the square opening facing down. Air can circulate, but rain stays out. Rectangular ports are more difficult, but rectangular bins do exist. When not in use the bins stack for storage. Credit the idea to Don Street.